pwm: lp3943: Drop usage of pwm_[gs]et_chip_data()

Instead of distributing the driver's bookkeeping over 3 (i.e.
LP3943_NUM_PWMS + 1) separately allocated memory chunks, put all together
in struct lp3943_pwm. This reduces the number of memory allocations and
so fragmentation and maybe even the number of cache misses. Also
&lp3943_pwm->pwm_map[pwm->hwpwm] is cheaper to evaluate than
pwm_get_chip_data(pwm) as the former is just an addition in machine code
while the latter involves a function call.

Link: https://lore.kernel.org/r/20230705080650.2353391-5-u.kleine-koenig@pengutronix.de
Signed-off-by: Uwe Kleine-König <u.kleine-koenig@pengutronix.de>
Signed-off-by: Thierry Reding <thierry.reding@gmail.com>